Apple Inc. has a long reputation for disrupting the markets with new innovations, and the Silicon Valley tech giant is now skirting the edges of one very traditional field: cardiology.

Heart doctors and traditional medical technology companies appear to be keeping an open mind so far as Apple launches a massive 500,000-person research study to see whether the Apple Watch can detect signs of the potentially serious medical condition called atrial fibrillation.

“AFib” is a chaotic, out-of-sync heartbeat that can damage the heart and allow blood clots to form that travel to the brain, where they can lead to strokes. Although many people do not know they are affected, the Centers for Disease Control and Prevention says the condition contributes to more than 130,000 deaths per year and costs about $6 billion annually in the U.S.

Apple said last week that it’s launching the Apple Heart Study in collaboration with the Bay Area’s Stanford University School of Medicine. Researchers will examine how well the four green LED heart-rate sensors embedded in the Apple Watch can screen wearers for signs of AFib, compared to a traditional electrocardiogram (ECG).

A person at Apple who is familiar with the project said Monday that if the study goes as planned, Apple plans to submit the study data to the Food and Drug Administration (FDA) to get marketing clearance for the software portion of the system. There are also plans to publish the final study data, but the company declined to provide details about its early work to validate the system.

The system gathers real-time optical observations of blood flow through the skin, and runs the data through an algorithm designed to isolate a fibrillating heartbeat from other signals and “noise” that the sensor picks up. If the user has downloaded the Apple Heart Study app and joined the study, they will get an alert if their heart rhythm appears abnormal. Alerted users can receive a free telemedicine screening with a study doctor, plus a device that will take an ECG reading of the heart’s electrical activity.

Unlike a traditional clinical trial, which requires meeting with a doctor, participants in the Apple Heart Study can enroll just by downloading an app in the U.S. and having internet access on their phone. The study is approved by an institutional review board.

The study listing in, which was added over the weekend, said the effort aims to enroll as many as 500,000 users over the age of 22 to collect data through January 2019. Participants must have access to an iPhone 5s or later with at least iOS 11.0 and an Apple Watch Series 1 or later. Participants will be excluded if they have a self-reported diagnosis of AFib or heart palpitations known as “atrial flutter” or are currently taking anti-coagulation drugs.

Although the Apple Watch is advertised as being able to measure a user’s heart rate, it is not a medical device — a point emphasized by companies that make certified medical devices, such as longtime Minnesota cardiology device maker Medtronic.

“While the eventual impact of new atrial fibrillation detection screening technologies is yet to be determined, Medtronic supports proactive screening for AFib that allows people to seek medical care and early diagnosis,” Medtronic said in a statement. “Notably, consumer wearable technologies provide a generalized screening approach, but ultimately require additional monitoring to obtain actionable diagnoses to guide clinical care.”

Medtronic sells an implantable heart monitor called the Reveal Linq that is cleared by the FDA to monitor for irregular heart beats such as atrial fibrillation with a high degree of accuracy. If the company was concerned about losing any Linq sales to Apple Watches, it didn’t say so when asked.

Last week the FDA also cleared its first medical device accessory for the Apple Watch — a device called the Kardia Band, made by California’s AliveCor. The device uses what AliveCor calls artificial intelligence and cloud computing to detect when a person’s heartbeat is out of sync with their current physical activity, and then notifies the user to take an ECG reading on the single-electrode ECG reader mounted in the $199 Kardia Band.

The ECG data are then displayed on the Apple Watch and captured for later analysis by a physician. AliveCor also makes a $99 FDA-cleared portable ECG reader called the Kardia Mobile, which is compatible with Android and iOS systems and can be attached to the back of a smartphone.

Stanford also runs its own app-based cardiac study called MyHeart Counts, which is among many different medical and fitness-related applications listed in Apple’s App Store. Apple has encouraged the development of medical-research apps by releasing an open-source software framework called ResearchKit, which has been used to design apps related to everything from autism to melanoma to postpartum depression.

Regulators have urged consumers to approach medical apps with some skepticism. The Federal Trade Commission settled a lawsuit last December with California-based Aura Labs, which has claimed that its $4.99 Instant Blood Pressure app could give blood pressure readings as accurate as an armband cuff, even though clinical testing later found the app was much less accurate.

Still, doctors said that legitimate health-related smartphone apps can have value, by flagging potential cases that need professional care.

Dr. JoEllyn Moore, an electrophysiologist with the Minneapolis Heart Institute, said that in general, patients who go to the doctor when their Apple Watches send alerts about possible atrial fibrillation would most likely be given a routine heart screening with an onsite ECG machine. They may also get a small device to take ECG readings at home when they are having an AFib episode.

“It would be a similar screen for anyone who comes in complaining of an irregular heart rhythm,” Moore said.

The risk in technologies such as the Apple Watch’s heart-rate sensor test is that they may create false positives, inducing unnecessary anxiety in users and driving up overall health care costs without improving anyone’s health. Physicians and the tech industry will be watching closely to see whether the Apple Watch can keep false positives down while flagging previously unknown cases of AFib.

“It has the potential to be very exciting. I think time will tell how accurate this tool is going to be,” she said.